Reasons for cracking of fastening pipe joint nuts

The nut of a certain fastening pipe joint was cracked. The reasons for nut cracking were analyzed using macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscopy, and energy spectrum analysis. The results show that the microstructure of the nut showed the precipitation of chromium rich carbides along the grain boundaries, which reduced the material's resistance to intergranular corrosion. Corrosive media infiltrated the inner wall of the nut, and under the combined action of corrosive media and tightening force, the nut underwent stress corrosion cracking.